1. Field of the Invention
This invention relates to the reactivation of metallic hydrogenation catalysts and more specifically to the reactivation of palladium catalysts employed in the hydrogenation of reducible cyclic organic compounds.
2. Description of the Prior Art
In the hydrogenation of reducible cyclic organic compounds employing palladium catalysts, the presence of impurities which inhibit the desired hydrogenation reaction by poisoning the palladium catalyst is undesirable due to the uneconomical rates of hydrogenation which result from such inhibition. A class of impurities capable of inhibiting the hydrogenation of such reducible cyclic organic compounds which are especially disadvantageous are those which contain nitrogen. Such compounds, herein termed "deleterious nitrogen impurities," include, for example, ammonium salts, hydroxylamine salts, urea, tertiary amines, primary amines, and polyamines. Such impurities may be introduced into the hydrogenation reaction mixture from a variety of sources. For example, while phenol may be successfully treated by the process of U.S. Pat. No. 3,692,845 to remove carbonyl impurities prior to hydrogenation, the recovery of phenol from the purification step as by distillation may cause the inadvertent transfer of the polyamine to the recovered phenol, thereby introducing the polyamine as a deleterious nitrogen impurity into the hydrogenation reaction mixture. While processes such as that disclosed in U.S. Pat. No. 3,824,193 have been developed for reactivation of particular metallic hydrogenation catalysts employed in specific hydrogenation systems, the requirements in such processes of heating the catalyst prior to its recycle to the hydrogenation mixture is disadvantageous due to the added expense which such heating steps entail and to the possible degredation of the catalyst as a result of such heating treatments. Another process employed in the treatment of spent catalysts is that process which is described in U.S. Pat. No. 2,692,240.